cramps are very normal in early pregnancy...I had them til around 10 weeks.....totatlly normal it's just your uterus stretching and your baby implanting
yes, having children that close together can cause some complications. Not to scare you of course. Your body is still adjusting to getting the last one out. However, everything may be just fine. I would go to the doctor and explain these cramps, it could just be muscles stretching out again.